The problem with going to the 1 lens does it all thing, is that you lose a lot of different things to gain the convenience. For example, the quality of the lens isn't quite as good and its also slower, espeically at the long end. The 28-300 is an f/3.5-6.3 which means that its widest aperture is f/3.5, but only at the 28mm end and maybe to about 40mm. f/3.5 isn't to bad, however, the f/6.3 at the long end is very small. That will probably be from about 220mm or so to 300mm. It 1/3 of a stop smaller than the 75-300mm f/4-5.6 at the 300mm end. For both lenses I would say that f/4 around 75mm is probably the same. (f/# tells you the size of the hole in the lens that lets light in, works like the pupil of your eye. The bigger the hole {since the numbers are fractions, the small the number, ie: 1/5.6 is bigger than 1/6.3} the more light is let in and will allow for a faster shutter speed. Faster shutter speed means being able to get more of a stop in the action instead of slight blur's of the legs and/or arms of the players.) This is why you see the camera people at sporting events with those BIG HUGE lenses. They have a bigger hole, therefor needing the lens to be big to accomodate that size hole. Many of them may be the same 300mm length, but their f/number is probably f/2.8 compared to the f/5.6. That is a HUGE difference in size. Kind of like comparing the size of a 1/2 dollar to a dime.
Typically the 1 lens does it all lens will be slower to auto focus and may hunt for a focus more often than a smaller range lens. Thus you may lose more shots.
I wouldn't worry to much about the XR Di LD stuff.
If anything you'd be better off saving a bit more and getting the Nikkor 70-300mm f/4.5-5.6G ED-IF AF-S VR lens. It is very sharp, focus' very quick and has the added bonus of VR (Vibration Reduction). What the VR will do in your shooting scenerio is help keep the lens still, not getting extra blur from camera shake. That is the biggest reason I bought this lens. 1/2 my pics at the 300mm end were wasted because of camera shake. Holding a camera steady at the 300mm isn't all that easy. VR makes it much easier.
This may be a bit more information that you wanted, so I hope I didn't confuse you any further.
Keep asking questions. We'll help as best we can.